ORIGINAL: TFOX
I would be skeptical of this design in the first place.It isn't even designed to open until well after it is inside the animal.
Again I say,not all mechanicals are created equal.
This kind of shows what I think happened. I think the arrow went through a section of hide high or low and exited as it opened then the fletch caught the small entry wound and stopped the arrow closing the blades.
That BH design lookes like a real energy stealing design. Meaning it takes a huge amount of energy away from the arrow to open the blades. ...Not one I'd shoot.